Transition from bottle to sippycup advice

Favi • Baby boy arrived 07/12/2019 💙 First time mom❤️

So my bubs still isn’t off the bottle at 14 months in a couple weeks. I’m still having trouble on how exactly to do it ? I’ve introduced it during the day for milk but what other times should I offer it to him ? And I read that offering milk at naps or night cap cause tooth decay ?! But he still needs milk/formula at night ! Any suggestions? I’m kinda lost 😢